Test 2 Flashcards
Bateman Equation
Ad=Ap(0)(e^(kpt)-e^(kdt))kd/(kd-kp)
Where p = parent, d = daughter. Note also that Ad(0)e^(kdt) is activity of parent over time.
Definition of Reference Man
As originally defined in ICRP 23 (but later changed in ICRP 89): 70kg, 170cm, Caucasian, living in 10~20C, and 20~30 years old.
Snyder-Fisher Mathematical Model
Used for calculating dose in other organs due to source organ emitting radioactivity. A phantom was created to represent this model.
Exposure, Dose, Equivalent Dose, and Effective Dose calculation
Dose D = exposure X * constant
Equivalent dose H = Beam Quality Q (ICRP 26) * D
or Radiation Weighting Factor Wr (ICRP 60) * D
Effective dose E = sum (Tissue Weighting Factor * H) for all tissues involved
ICRP 30 (~1980)
Includes Part 2 and addendum on Part 4: “Limits for Intakes of Radionuclides by Workers.”
ICRP 26 (1977)
This publication of ICRP introduced quality factor for ionizing radiation, introduced dose equivalent, effective dose equivalent, and set up basic internal dosimetry concepts.
ICRP 26 Formulation of Internal Dosimetry
Source and target organs concept introduced. Absorbed fraction concept introduced (absorbed energy / emitted energy). Quality factors defined for beta, alpha, neutrons, and gamma. Tissue weighting factor defined. Equivalent dose for 50 years, H50 = sum (Quality factor * dose for 50 years), defined.
ALI (Annual Limit on Intake)
Activity of nuclide taken in that would itself alone result in EFFECTIVE DOSE (not equivalent!) of 50 mSv (annual dose limit). ***UNIT: Bq/yr
Stochastic Limit for ALI Calculation
Assume 50 mSv 50-year EFFECTIVE DOSE limit to calculate ALI in Bq/yr. We can do so by dividing 50 mSv by effective dose per decay!
Nonstochastic Limit for ALI Calculation
Assume 500 mSv 50-year EQUIVALENT DOSE (H50=Wr * D) limit to calculate ALI in Bq/yr. We can do so by dividing 500 mSv by equivalent dose per decay!
NOTE: LENS OF EYE is an exception! Assume 150 mSv limit!
Solving for H, Equivalent dose given for 50 years
H = k * U * SEE, where U = # of decays, SEE = specific effective energy (equivalent dose per transformation, Wt * D / Bq), and k = constant for energy conversion
Specific Effective Energy Calculation
SEE = sum over different radiation types (Quality Q * Radioactive Yield Y * Energy Emitted E * absorbed fraction AF(T<-S) / Mass of Tissue M).
Basically, equivalent dose per decay on target organ T. May result in MeV/g.
Convert to Sv: SEE (MeV/g) * (1.6*10^-10) = SEE (Sv)
Quality Factors for various radiation sources (ICRP 26)?
Beta, gamma = 1
Fast neutron, proton = 10
Alpha, fission fragments = 20
Absorbed Fraction AF for SEE Calculation
Can be reasonably determined: AF = 1 for beta, alpha for S<-S; if target is sufficiently far away, AF =0 since beta/alpha stops in less than 1 mm in tissue.
formula for effective half-life given biological clearance half-life Tb and physical decay rate Tr
Teff = Tr * Tb / (Tr + Tb)
Note: this looks like effective mass, doesn’t it?
Three Mile Island 1979
43,000 Curies Krypton but less (15 Curies) of Iodine-131 released. 2 mrem within 50 miles of TMI to 2 mil.
1 mCi = ? MBq
37 MBq
Chernobyl 1986
Over 100 rad to 200 workers; over 400 rad to 30 workers (all dead); average of 20 rem to within 200 miles of the reactor, population of 272,800.
I-131: 17 million curies
Cs-137: 2 million curies
Tritium Exit Signs
Originally 15 Curies, self-luminating exit sign. Sold in US, still circulating.
Solubility in Tissue of Common Isotopes
Tritium: 0.02 ; Xenon: 0.1
How do you calculate equivalent dose rate dH/dt for people immersed in radioactive gas? Give three equations, one for external radiation due to surrounding gas, one for absorbed gas in tissue, and one for lung from inhaled gas.
Dose derived from activity concentration, Bq/g = (Bq/cm^3) / (g/cm^3)
External radiation: dH/dt = g(e) * k * C/p * s, where k is ratio of stopping powers in air versus in tissue k~1, C/p is activity concentration in Bq/g, and s is equivalent dose rate Sv/hr of air per Bq/g
Absorbed gas in lung: dH/dt = g(a) * [delta * C/p] * s, where delta is solubility
Air in lung: dH/dt = g(L) * C / (M/V) * s, where p is replaced with mass of lung and volume of AIR in lung
Xenon-133
Specific gamma constant: 0.15 Rcm^2/mCihr
So exposure = gamma * activity / distance^2. Biological half life 2 min, physical half life 5.27 days.
What is Cumulated Activity for instantaneous uptake? What is the formula for it?
Activity integrated over infinite time (total disintegrations)
A = Ao * 1.44 * Teff
where Teff is effective half life.
Find integral dose from cumulated activity.
Integral dose (g*rad) = A (uCi*hr) * delta, where delta is conversion from cumulated activity A to energy (g*rad is a unit of energy). This equation only applies if we assume all energy is absorbed by source organ.
What is Cumulated Activity for non-instantaneous uptake? Formula?
A = Ao * 1.44 * Teff * (Tue/Tu),
where Tue = Tu*Tp/(Tu+Tp). Notice how as Tu -> 0 (instantaneous uptake), Tue/Tu -> 1.
What is formula for delta, disintegration-to-energy conversion factor? (Used to calculate gramrad from uCihr)
delta = 2.13 * Y * E (gramrad/uCihr),
where Y = emission ratio (100% or less), E = energy emitted in MeV
Specific absorbed fraction
Absorbed fraction of dose released from source to target PER gram of target organ. = AF / mass of target.
Reciprocity theorem
Specific absorbed fraction is equal for source organ and target organ even if the source and target are switched. That is, AF(S<-T) / mass of source.
Mean Dose per Cumulated Activity, S
S(T<-S) * delta / m_T ].
MIRD Stands for?
Medical Internal Radiation Dose
ICRP vs MIRD compare and contrast
ICRP concerned with hereditary effects, RISKS of cancer; MIRD concerned more with radiopharmaceutical diagnostics/therapy, and now with voxel tomographic models and deterministic effects of dose.
Tritium Facts
Max E: 0.018MeV, Half-life: 12.3 yrs
Dose of non-penetrating radiation to internal organ
D = 19900 * Concentration * E * Teff * (1 - f) C = MBq/g, E = avg energy, 1-f = fraction decayed
Conversion from MeV/g to mGy
1.602 x 10^-7 mGy = 1 MeV/g
Physical Stage of water in ionizing radiation
In this stage, water is either excited or ionized. Occurs in less than 10^-15 second.
Prechemical Stage of water in ionizing radiation
In this stage:
Excited water: H2O* -> .OH + H. or -> H2O+ + e-
Electron is dissolved: e- -> e- aqueous.
Occurs 10^-15 to 10^-12 second.
Chemical Stage of water in ionizing radiation
In this stage:
Radicals combine and aqueous electrons attack atoms.
Occurs in 10^-12 to 10^-6 second.
In tissue, the radicals survive for ~0.1 to 1 us.
Oxygen Enhancement Ratio (OER)
Dose needed to achieve LD50 in hypoxic environment / Dose needed to achieve LD50 in oxygenated environment > 1
Diffusion constants for radicals
(Multiply by 10^-5 cm^2/s) OH 2; e- 5; H3O+ 8; H 8
Dose Modifying Factor (DMF)
DMF > 1. Dose to LD50 with radioprotectors / Dose to LD50 without radioprotectors
Four types of radiation effect
Somatic, hereditary, stochastic, nonstochastic
Non-stochastic effects
erythema, tissue burns, cataract, sterility, acute radiation syndromes, and death
Acute Radiation Syndromes: Hematopoetic Syndrome
1Gy or greater to blood. Latent period of 4 weeks. Cause of death: infection, dehydration. Prominent symptom: loss of lymphocytes and neutrophils, and later RBC/platelets.
Acute Radiation Syndromes: Gastrointestinal Syndrome
> 6~8Gy to GI tract. Latent period of 3-5 days. Cause of death: uncontrolled passage of fluids, infection, electrolyte imbalance, within 4 to 10 days. Prominent symptom: Loss of appetite, ileus (obstruction), nausea & vomiting.
Acute Radiation Syndromes: Cerebrovascular Syndrome
> 20Gy to brain. Latent period of 12 hrs. Cause of death: brain swelling, inflammation (meningitis). Prominent symptom: disorientation, ataxia (incoordination), burning sensation, loss of consciousness.
Sterility non-stochastic dose limits
Ovaries: 10 rad, delay of menstruation. 200 rad, temporary sterility. 500 rad, permanent sterility.
Testes: 10 rad, drop in spermatozoa. 200 rad, temporary infertility. 500 rad, permanent infertility.
Radium Dial Painters Study
Ra-226 (alpha), Ra-228 (beta) used for glow-in-dark watch. ~80rad threshold for bone sarcoma, > 10uCi Radium risky.
High BKG (Background Radiation) Area Study
Global average is 100 mrem/yr, except radon. Studied Brazil, India, China with higher-than-normal BKG. 640 mrem/yr in Guarapari, Brazil due to monazite containing thorium, uranium. 380 mrem/yr in Kerala coast, India for 70,000 inhabitants. Guangdong, China at 550 mrem/yr for 73,000 people.
[ICRP 60, NRC] ICRP Limit on Committed EFFECTIVE Dose (not equivalent) due to ingested radionuclides vs. NRC Limit on Committed EFFECTIVE Dose.
Derived Air Concentration in Bq/m^3?
DAC = ALI(Bq) / 3000m^3 (a person breathes 3000m^3 per year)
I-131 production and half-life
Produced from Te-131m (half life 30 hrs), and I-131 has half life of 8.05 days
Roentgen to C/kg to Dose
1 R = 2.58 x 10^-4 C/kg =(multiply by 33.7 J/C of ionization)= 0.877 rad
Concept of Dose Equivalent introduced in what ICRP? What is quality Q?
ICRP 26. In ICRP 26, Q modifies radiation dose with stopping power. <3.5keV/um = Q = 1; ~7keV/um = Q = 2; 23keV/um = Q = 5 etc. Later replaced by ICRP 60 with w(R), radiation weighting factor.
Posting requirements
1.00 mSv/hr, high radiation area sign.
NRC Regulations: Parts
NRC Part 20: protection standards
NRC 10, Part 35: human
NRC 10, Part 71: RAM transport
The reference man was originally defined on which ICRP?
ICRP 23
Which ICRP and what parts established limits for intakes of radionuclides by workers?
ICRP 30, parts 2 and addendum on 4
Source (S) and target (T) organs defined in which ICRP?
ICRP 26
Equivalent Dose limit in ICRP 26
Lens of eye 150 mSv, all others 500 mSv. Note: this is EQUIVALENT DOSE limit, since it’s for each TISSUE. Remember, H = W(r) * D.
Molecules used for ventilation and perfusion lung scan
Xe-133 for ventilation, Tc-99m MAA for perfusion
Tissues with weight = 0.01 (ICRP 103)
skin, bone surface, kidneys, brain, salivary glands
Tissues with weight = 0.05 (ICRP 103)
bladder, liver, esophagus, thyroid, gonads
Tissues with weight = 0.12 (ICRP 103)
breast, bone marrow, stomach, colon, lung
ICRP 23 was divided into three major parts. What did each of the parts focus on?
- Anatomical values for reference man; 2. Gross and elemental values for reference man; 3. Physiological data for reference man
What proteins with Tc-99m are used in: 1. Skeletal imaging, 2. Liver imaging, 3. Lung perfusion imaging, 4. Kidney-Ureter bladder imaging?
- Skeletal: Tc-99m diphosphonate
- Liver: Tc-99m sulfur colloid
- Lung: Tc-99m macroaggregates
- Kidney/Ureter: Tc-99m DTPA
Identify organs identified as “principal organs” in MIRD “reference man”
brain, skull, spine, arm bone, ribs, lungs, heart, liver, kidneys, intestines, bladder, pelvis.
MIRD formulation of dose
D = A * S(T from S) is absorbed fraction. S(T from S) = sum (delta * AF(T from S) / m_T). And delta = 2.13 * E(MeV) * yield per decay.
MIRD Pamphlet No. 21 (2009)
Updated internal dosimetry schema and standardized nomenclature.
Mo-99 to Tc-99m decay scheme and half-life?
Mo-99 decays to Tc-99m via ß- decay, except 14% of the time. Half-lives are 66 hours for Mo-99, 6 hours for Tc-99m.
Dose in Gy that will produce cataract
> 10 Gy for 100% cataract development. Threshold now 0.5 Gy in 2011 publication on ICRP. Data gathered from MDCT perfusion studies + CSA.
Dose in Gy that will produce temporary hair loss
3~5 Gy
Stratum Basale
Stem cells on skin that are most affected by radiation
Dose in Gy that will produce erythema
300 rad - 1000 rad (3 to 10 Gy)
Subclinical < 1 Gy Effects
12cGy: sperm count decreases by 45 days
20cGy WHOLE body: dicentric chromosomes appear
75-100cGy: depression in bone marrow
Granulocytes
“Scavengers,” like macrophages that eat up cells. Neutrophils being one of them.
Lymphocytes
Secondary immune response cells (antibodies etc)
Compartment Model for radioactive intake introduced in what ICRP?
ICRP 30
